Autophagy is an ancient evolutionarily conserved pathway designed to maintain cellular homeostasis by degrading long-lived proteins and organelles in the cytosol. It is also used as a survival mechanism under starvation conditions. Recent studies demonstrated that autophagy is utilized by the cells of the innate and adaptive immune systems to combat viral infections. Innate recognition of viruses occurs via two distinct pathways. In professional viral sensors, the plasmacytoid dendritic cells (pDC), recognition of viruses occurs in the endosomes via Toll-like receptors (TLR) 7 and 9. Our recent work has demonstrated that autophagy plays a key role in recognizing signatures of viral infection in pDCs through TLR7. In contrast to pDCs, most other cell types of the body utilize cytosolic sensors of viral replication via RIG-I like receptor (RLR) family. Molecules involved in autophagy have been shown to block RLR signaling. In addition, recent reports indicate that autophagy delivers endogenous viral antigens to the MHC class II loading compartment, allowing activation of CD4 T cells. However, the relevance of such pathways during in vivo virus infection is unknown. In this application, we present preliminary data that reveal the requirement for Atg5, a key molecule required for formation of autophagosomes, in the transduction of signaling through TLR9 leading to the activation of type I IFN genes in pDCs upon herpes simplex virus (HSV;TLR9 agonist) infection. In addition, we show that autophagy negatively regulates RLR pathway in non-plasmacytoid dendritic cells upon vesicular stomatitis virus infection (VSV;RIG-I agonist). Finally, we demonstrate a key in vivo role for autophagy in the processing and presentation of various forms of antigens on MHC class II in dendritic cells upon HSV-1 infection. Building on these preliminary studies, we propose to examine the importance of autophagy in both innate and adaptive immune responses using a variety of molecular and cell biological techniques and using established mouse models of virus infection. In the first Aim, we will determine the mechanism by which Atg5 and/or autophagy mediates signaling through TLR9 upon HSV infection in pDCs through the use of molecular and cellular biological techniques. In the second Aim, we propose to determine how autophagy regulates RNA sensor activation upon VSV infection through proteomics and biochemical approaches. In the final Aim, we will interrogate how dendritic cells utilize autophagy for processing and presentation of extracellular viral antigens in vitro and in vivo in mice selectively deficient in autophagy within the dendritic cell populations. By providing basic understanding of how autophagy orchestrates the generation of innate and adaptive immunity against virus infections, these studies will help to establish important foundation with which to design vaccines and anti-infective measures against a variety of viral pathogens PUBLIC HEALTH RELEVANCE: While autophagy is an ancient evolutionarily conserved pathway designed to maintain cellular homeostasis by degrading long-lived proteins and organelles in the cytosol, recent studies from our group and others have revealed the role of autophagy in the immune system. In this application, we propose to examine the importance of autophagy in both innate and adaptive antiviral immune responses using well-established genetic, biochemical and cell biological tools as well as in vivo animal models of both RNA and DNA virus infections. The understanding gained from the proposed studies will not only provide scientific advances in how autophagy is utilized by the immune system, but also to help establish critical foundation with which to design immunological interventions and preventative measures against a wide variety of viral diseases.